The primary aim of this proposal is to extend and explore our finding that potentials recorded during cardiac depolarization are strongly influenced by orientation of cardiac fibers. Traditional application of volume conductor theory has been based on the assumption that the generators during depolarizaton of ventricular muscle. Our studies have indicated that during depolarization the generators are, rather, oriented nearly parallel to the long axes of cardiac fibers. Because of this, the fields produced external to the wave of depolarization are markedly different from those which would be predicted by the conventional assumption. Indeed, an approaching wave of depolarization will frequently generate a negative rather than a positive potential (transverse approach). These findings appear to account for the fact that there have been no satisfactory predictions of electrocardiographic potentials from depolarization pathways. Our demonstration of the "axial dipole" orientation must be extended to blocks of tissue which are isolated so that there is activity in only one section of myocardium. A second step will extend this finding to blocks of tissue which are depolarized through Purkinje fibers. Finally, we will predict cardiac surface potentials from depolarization pathways.